1. Field of the Invention
The present invention relates generally to detection methods and apparatuses and particularly to detection methods and apparatuses detecting embedded data from image data.
2. Description of the Related Art
There is known a technique used to detect embedded data from an image having data indicating a copyright holder or the like embedded therein in a background of an original image of characters or the like in the form of a woven pattern.
A technique used to detect embedded data is disclosed for example in Japanese Laid-Open Patent Publication No. 2000-059610. More specifically, an image is scanned to obtain image data, which is in turn divided into rectangles of a predetermined size and therefrom embedded bit data is extracted and if an extracted bit string satisfies a condition added in embedding the data for determining a rectangle's position, the bit string is handled as a candidate result of decoding, and if there are more than one such candidates, majority logic is performed for each bit to adopt a more reliable bit value as a result of decoding.
Furthermore, an earlier patent application filed by the Applicant and published as Japanese Laid-Open Patent Publication No. 2007-096503 discloses that to achieve an increased processing speed, image data obtained from a scanned image is divided into a plurality of blocks and therefrom local data is extracted and whether information can accurately be read for each predetermined number of blocks is determined, and if so, the information is read.
However, these documents disclose techniques assuming detecting one type of data embedded in an original of a single sheet. If an original of a single sheet having a plurality of types of data embedded therein or two or more originals each having different data embedded therein have their embedded data detected, the detection provides a result indicating each data mixed up, and the embedded data cannot be detected accurately.